Write as the sum or difference of x, y, and z:?

Question

{2y^4√x/a^4}

y is raised to the 4th power

yes sorry there is a log involved it is log 6 {2y^4√x/a^4}

Answer 1

2y^4√x/a^4 cannot be simplified.
"Write as the sum or difference" makes me think that there might be a log involved.
For example,
log(2y^4√x/a^4)
= log(2y^4√x) - log(a^4)
= log(2y^4) + log(√x) - log(a^4)
= log(2) + log(y^4) + log(x^(1/2)) - log(a^4)
= log(2) + 4log(y) + (1/2)log(x) - 4log(a)

Answer 2

What's z?

Either there's important information still missing, or the answer is no.